1. Field of the Invention
The present invention generally relates to a light emitting module, and more particularly, to a light emitting module using light emitting diodes (LEDs) as a light source and a surface light source device in which the light emitting module is applied to.
2. Description of Related Art
Recently, with an increased in the light emitting efficiency of the LED, the LED has gradually replaced the fluorescent lamp and the incandescent lamp in some fields, such as the backlight module of the liquid crystal display (LCD).
FIGS. 1A and 1B are schematic diagrams showing a side emitting light emitting devices disclosed in the U.S. Pat. No. 6,598,998. The conventional light emitting module 100 comprises a light guide member 110 and a plurality of side emitting light emitting diode (LED) package structures 120. The light guide member 110 has a plurality of through holes 112, and the LED package structures 120 are embedded in the through holes 112. Besides, each LED package structure 120 comprises a carrier 122, an LED chip 124 and a lens part 126. The LED chip 124 is arranged on the carrier 122, and the lens part 126 encloses the LED chip 124.
According to the above description, the LED chip 124 is suitable for emitting a light, and the lens part 126 has a reflection surface 126a and a plurality of refraction surfaces 126b. The light emitted from the LED chip 124 is reflected by the reflection surface 126a and refracted by the refraction surface 126b, and then the light emerges from a side of the lens part 126 and is incident into the light guide member 110 (such as a light beam 50). Next, the light beam 50 undergoes total internal reflection many times within the light guide member 110 and then uniformly emerges a light emergent surface (not shown herein) of the light guide member 110.
In the conventional light emitting module 100, the propagation direction of the light beam 50 is not well guided, and the light beam 50 undergoes total internal reflection many times within the light guide member 110, such that the light emitting efficiency is lowered. Besides, the LED package structure 120 of single side light emitting only emits a light beam with a single wavelength, and there is a need to combine different LED package structures 120 of different wavelengths to generate white light. However, this would increase the cost and requires a larger space for mixture of the light, and therefore the volume of the conventional light emitting module 100 is larger. Additionally, the cost of the LED package structure 120 of side emitting is higher to result in a higher fabrication cost of the light emitting module 100.